Coloring leather



United States Patent 3,414,366 COLORING LEATHER Lars E. Nordstrom, Linden, and John F. Wagoner, Williamsport, Pa., and Robert M. Lollar, Sheboygan, Wis., assignors to Armour and Company, Chicago, Ill., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 287,183, June 12, 1963. This application Nov. 12, 1963, Ser. No. 323,150

8 Claims. (Cl. 8-12) ABSTRACT OF THE DISCLOSURE Leather, such as aldehyde-tanned and resin-impregnated leather, is colored by dissolving dye in a solvent miscible in all proportions with water to form a watersolvent solution and the leather is immersed in the solution. Pressure of about 50-400 pounds per square inch is applied to the leather to compress the leather to about -15 percent and to force the dye solution through the resin into the leather, the leather being repeatedly compressed and released to knead the dye solution into the leather.

This invention relates to coloring leather, and is particularly useful in the coloring of aldehyde-tanned leather in a solvent system and leather impregnated with resins in a solvent system.

This application constitutes a continuation-in-part of our copending application, Ser. No. 287,183, filed June 12, 1963, now abandoned.

The problem of dyeing leather is made considerably more difficult when the leather is aldehyde-tanned and impregnated with resin in a solvent system. For example, a white sole leather which is formaldehyde-tanned and impregnated with a hydrocarbon resin, polybutene, and paraffin wax in a solvent system is extremely difficult to dye, even to a partial extent. Apparently, the resin in the leather acts as a repellent to dye, and satisfactory coloruptake cannot be obtained within practical periods of time by present dyeing methods.

A primary object, therefore, of the present invention is to provide a method for dyeing leather, including treated leathers, such as aldehyde-tanned and resin-impregnated leathers. A further object is to provide a method for treating leather in which water-miscible solvents for dye are employed with the selected dye and in combination with pressure and release steps for obtaining substantially complete coloring of the leather. Another object is to provide a method in which a dye solution is applied to leather and the dye caused to penetrate completely the leather by repeated kneading operations. Yet another object is to employ alcoholwater systems as dye solvents, together with pressure operations for substantially complete penetration of resin-impregnated leather. Other specific objects and advantages will appear as the specification proceeds.

In one embodiment of our invention, we dissolve the dye in a solvent which is miscible with water in all proportions, and apply the dye solution to the leather and knead the dye solution into the leather. The leather may be immersed in the dye solution and pressure applied to the leather and released while the leather is immersed in the solution, the pressure and release bein a single operation or repeated operations. Alternatively, the dye solution may be applied to the leather, -as by dipping, swabbing, fiow coating, spraying, etc., and the dye solution caused to impregnate the leather by kneading the leather with any suitable mechanical or pneumatic pressure device through any frequency or rapidity of cycle effective for causing the dye solution to penetrate the leather material.

Any suitable means for applying pressure and releasing the same may be employed, as, for example, a press, nip rollers, or other squeezing or pressure devices.

The pH may be adjusted up or down, depending upon whether the dye is anionic or cationic. The temperature may be varied as desired within wide limits, room temperature being satisfactory. After the application of the dye solution to the leather and the pressing operation, the fixing and rinsing of the dye may be accomplished by establishing common methods, such as by the use of alkali or acid conditions.

In practicing our process, we prefer to employ any suitable dye solvent which is miscible with water. We prefer to employ ethyl alcohol in alcohol-water concentration of 50 to 90 percent, isopropyl alcohol in a concentation of 40 to 90 percent, and n-propvl alcohol in a concentration of 40 to percent. Methyl alcohol may be used in the proportions of 40 to 100' percent. It will be understood that the solvent proportions may be varied substantially when employed with different dyes and depending on the thickness of the leather being colored, but for general purposes we prefer the alcohol concentrations set out above.

Optimum concentrations of the alcohol-water solvents were for ethyl alcohol about 60 to 70 percent, for isopro yl alcohol about 50 to 60 percent, for n-propyl alcohol about 50 to 60 percent, and for methyl alcohol about percent.

In the pressing operations as described above, a plate press, such as a Carver press, provides satisfactory results. Nip rollers-may also be employed, and it is preferred to pass the leather in a uni-directional path between the rollers. If desired, the leather may be placed in a plastic bag with the dye solution present, the bag being sealed and passed through a wringer equipped with rollers. When successive pressure applications are made, it is found that the pressure requirements may be reduced. In general, however, we find that a pressure of from about 50 to 400 pounds per square inch gives satisfactory results, and when coloring thicknesses of leather up to 0.3 inch we prefer to employ pressures of from to 300 p.s.i.g. While the extent of compression of the leather will vary depending upon its porosity and thickness, etc., in general we find that the pressure applied should be such as to reduce the thickness of the leather by five to fifteen percent.

Specific examples illustrative of the process may be set out as follows:

EXAMPLE I 1.0 g. Kiton Brown R (Color Index No. 14625: Acid Brown 7) was dissolved in 50 ml. of water at 80 C. The solution was then diluted with 50 ml. of ethyl alcohol to which had been added 5 ml. of ammonium hydroxide. The solution and a piece of leather, in this case formaldehyde-tanned leather impregnated with a hydrocarbon resin, polybutene, and parafiin wax (in a solvent system), were placed in a container and the leather subjected to a pressure of 200 lbs. per square inch in a Carver laboratory press for a period (dwell time) of 10 seconds. The application of the pressure was repeated two more times for a period of 10 seconds each. The piece of leather was then placed in a fixing bath containing water and 5 percent of formic acid by volume for a period of 30 minutes. It was then rinsed by immersing in water at room temperature for 30 minutes and then dried overnight at room temperature. The leather was found to be uniformly dyed from grain to flesh.

3 EXAMPLE 11 1.0 g. Bismark Brown G/ (Color Index No. 21000: Basic Brown 1) was dissolved in 50 ml. of boiling water and diluted with 50 ml. of ethyl alcohol to which had been added 5 ml. of formic acid. This solution and a piece of leather, in this case, formaldehyde-tanned impregnated leather similar to the leather treated in Example I, were placed in a plastic bag and sealed. This plastic bag containing the leather and the dye solution was then put through the rollers of a laundry-type wringer five successive times. The dye solution was then changed to a fixing solution of water containing 5 percent ammonium hydroxide by volume, the bag rescaled, and the rolling operation carried out three times. Finally, the leather was removed from the bag and rinsed by immersing in water at room temperature for 30 minutes. It was then dried at room temperature overnight. The resulting leather showed complete penetration of the dye from grain to flesh.

EXAMPLE III One percent Kiton Brown R dye (CI. 14625) was dissolved in ethyl alcohol batches of 50, 60', 70 and 80 percent concentration, and a leather body of 0.3 inch in thickness was treated by the rolling technique and finishing steps described in Example II, and a completely struck-through color (grain to flesh) obtained.

Similar tests were made with isopropyl alcohol and n-propyl alcohol with comparable results.

Using the pressing technique and other steps as described in Example I, complete penetration of the leather was obtained using ethyl alcohol in the concentration range 50 to 90 percent, with isopropyl alcohol 40 to 90 percent, and n-propyl alcohol 50 to 60 percent.

EXAMPLE IV The process was carried out as described in Example I except that ammonium hydroxide was omitted from the dye solution and the pressing operation was carried out at 300 pounds per square inch, pressing only once for a 15-second dwell time. The tests were carried out at room temperature instead of at elevated temperatures as described in Example I. Complete penetration was obtained with 40 to 90 percent ethyl alcohol. Successful results were also obtained with isopropyl alcohol and npropyl alcohol.

EXAMPLE V Tests were carried out with a leather split to .225-.250 inch. The leather was formaldehyde-tanned and resinimpregnated in a solvent system. One percent of anionic dye (Metanil Yellow VS CI. 13065), having a molecular weight of 375 and an acid yellow 36 color index, was dissolved in ethyl alcohol concentrations of 40, 60 and 80 percent to which 5 percent ammonia was added, and the solution at a temperature of 50 C. was placed under pressure by the rolling technique described in Example II, the product being put between the rollers five successive times. The product was then immersed for 30 minutes in a 5 percent formic acid solution and later rinsed by immersion in water for 30 minutes. The leather was found to be uniformly dyed from grain to flesh.

Comparable results were obtained using isopropyl and n-propyl alcohol at the same concentrations of 40, 60 and 80 percent.

EXAMPLE VI The process was carried out as described in Example IV except that one percent of a dye (Methylene Blue D. Cone. (CI. 52015) having a color index of basic blue 9 and a molecular weight of 457) was used. Results comparable to those described in Example IV were obtained for ethyl, isopropyl and n-propyl alcohols at concentrations of 40, 60 and 80 percent. Methyl alcohol was also found to give complete penetration when the methyl alcohol was used at concentrations of 40 to 100 percent.

EXAMPLE VII The process was carried out as described in Example I except that the leather was formaldehyde-tanned in a solvent system. The results were comparable to those obtained in Example I.

EXAMPLE VIII The process was carried out as described in Example I except that the leather was impregnated with a hydrocarbon resin in a solvent system, and the results were comparable to those of Example I.

EXAMPLE IX Three grams Kiton Brown R (Acid Brown 7) and 7 grams naphthalene syntan (Tamol SD) were dissolved in 500 ml. of water at C. The solution was then diluted with 500 ml. isopropyl alcohol and the temperature maintained at 60 C. A sole was dipped in the dye solution for 10 seconds and then put through the rollers of a laundry-type wringer. The dipping of the sole in the dye solution followed by the squeezing between the rollers was repeated four times. The sole was then immersed in a water solution containing 5% formic acid for 3 minutes, squeezed between the rollers, rinsed in a water bath for 3 minutes, squeezed again between rollers, and finally dried in a drying chamber. The resulting sole showed complete penetration of the dye from grain to flesh.

EXAMPLE X The application of the dye solution to the sole was, in this case, made with a swabbing method. Instead of dipping the sole in the dye solution, the sole was wetted on grain and flesh sides using a cloth. Squeezing the sole between rollers was made after each swabbing. Five consecutive swabbings and squeezings were made. Fixing, rinsing and drying were applied as described above. The resulting sole showed completed penetration of the dye from grain to flesh.

EXAMPLE XI The application was, in this case, secured by pouring the solution over the sole, simulating a flow coat operation. Five consecutive pourings and squeezings were followed by the fix, rinse and drying. The resulting sole was completely penetrated by the dye.

In tests made with the various dyes, it was found that the dye must be one which is soluble in the solvent in order to obtain the desired results. Using a dye which is completely soluble in the alcohol-water solvent and using the pressures described, it was found that the dye solution could be effectively kneaded into the leather and that the leather could be uniformly dyed from grain to flesh, even though the leather had been resin impregnated, as described above.

While in the foregoing specification we have set forth specific steps and treating materials in considerable detail for the purpose of illustrating embodiments of the invention, it will be understood that such detail or details may be varied widely by those skilled in the art without departing from the spirit of our invention.

We claim:

- 1. In a process for coloring formaldehyde-tanned sole leather impregnated with a hydrocarbon resin, the steps of dissolving a dye in an alcohol solvent miscible in all proportions with water to form an aqueous dye solution, immersing the sole leather in said solution, and applying pressure of about 50-400 pounds per square inch to the leather.

2. The process of claim 1 in which the solvent is ethyl alcohol having an alcohol-water concentration of 50-90 percent.

3. The process of claim 1 in which the solvent is tion of 40-90 percent.

4. The process of claim 1 in which the solvent is npropyl alcohol having an alcohol-Water concentration of 40-80 percent.

5. The process of claim 1 in which the solvent is methyl alcohol having an alcohol-water concentration of about 90 percent.

6. The process of claim 1 in which the pressure is about 200-300 pounds per square inch.

7. In a process for coloring sole leather impregnated with hydrocarbon resin, the steps of dissolving a dye in an alc0h0l-water solution in which said alcohol has a concentration of about 40-90 percent, wetting the sur face of the leather with said dye solution, and then repeatedly compressing and releasing said sole leather under a pressure of about 50-400 pounds per square inch to cause the dye solution to completely penetrate said leather.

8. The process of claim 7 in which the leather is compressed to about 5-15 percent in thickness.

References Cited UNITED STATES PATENTS 1,090,799 3/1914 Spigno 812 X 1,729,938 10/1929 Harris 812 1,569,562 1/1926 Moog 8l2 X 1,843,740 2/1932 Schubert 812 X 2,204,262 6/1940 Stern 812 2,876,130 3/1959 Ciaccio 8-20 X OTHER REFERENCES Chemical Abstracts, vol. 22, 1928, p. 2076.

Lamb: Leather Dressing, pp. 138-141 and 98-99, pub. 1909 by Lea. Trades Pub. Comp., London, England.

El-Mariah et al.: J. Soc. Lea. Trades Chem. 1963, vol. 47, 131.

Zimmerman et al., Textile Research J., October 1948, pp. 615-627.

0 NORMAN G. TORCHIN, Primary Examiner.

D. LEVY, Assistant Examiner. 

